To perform this retention function, it is known to use an annulus whose radially inner edge is received in an annular groove of the downstream face of the rotor disk and whose radially outer edge bears against the downstream ends of the roots of blades that are engaged in axial grooves in the periphery of the disk.
The radially outer edge of the annular groove in the disk and the radially inner edge of the annulus are of complementary festooned or crenellated shapes, thus enabling the annulus to be brought into the annular groove of the disk by being moved in axial translation when the solid portions of the festooned edge of the annulus are in alignment with the gap portions of the festooned edge of the annular groove, and then to secure the annulus axially in the annular groove by turning it so that the solid portions of its festooned edge come into alignment with the solid portions of the festooned edge of the annular groove of the disk, which then bear thereagainst.
On its face facing towards the blade roots, the radially outer portion of the annulus has studs for engaging in corresponding cavities in the blade roots and which serve to prevent the annulus from turning about its axis.
In the locking position, the annulus is held axially by its portions bearing against the blade roots, against the downstream face of the disk, and against the festooned edge of the annular groove in the disk. To bring it into this position by turning it in the annular groove, it is necessary to deform it by pulling its radially outer portion axially and by pushing its radially inner portion axially, respectively to move the above-mentioned studs away from the ends of the blade roots until the studs are in register with the cavities that are to receive them, and in order to cause the solid portions of the festooned edge of the annulus to pass into the annular groove of the disk.
Such assembly is complicated to perform and requires the use of special tooling. Since the annuluses must withstand very high temperatures and since they are made of a sintered material that is very sensitive to scratching (where such scratches constitute crack starters and can greatly reduce the lifetime of the annulus), it is necessary to take great precautions to avoid damaging the annuluses while they are being mounted on the disk.
In addition, the studs must be machined and formed in the material of the annuluses, which is lengthy and extremely expensive. It is also necessary to machine the cavities for receiving the studs at the ends of the blade roots, and that also increases costs.